I have made .zsync files for all extensions in 2.x and 3.x. Also I make them for new extensions before uploading. Therefore when zsync.tcz is installed in your system, you will get the benefit of zsync when using the update function of Appsaudit. In other words, it is like with rsync and only the changed parts of extension files are downloaded. In the case of an extension like openoffice3.tcz, a change in the extension may only affect the menu entry or icon files. Without zsync, you would have to download the entire new 168MB extension to update it. With zsync, the difference that is downloaded may only be measured in kilobytes in that case. Possibly a huge savings in bandwidth when updating extensions.